Well based on Tested hardware and operating system list the largest tested drive is 1TB. You'll need Firmware 1.4 to support total storage spage greater than 2TB. See http://www.intel.com/support/motherboards/server/ss4000-e/sb/CS-026274.htm.
I just put in 2-2TB drives (1 seagate and 1 hitachi) into slots 1+2. Initialized them as raid 0 and he saw something like 3981GB available space. I made public 2000GB (the max) and made home 1725-ish. After he restarted, I made the remaining space as a new shared folder of 257GB called public_257. I'm going to order 2 more 2TB drives and then rebuild as raid5. summary: I would say that the 2TB limit we read about in the documentation means the shared volumes are capped at 2TB and doesn't apply to total disk space of the raid. I sure wish I had a couple 3TB drives to try before ordering the extra drives.